The syntheses of new geometric isomers of vitamin A and carotenoids are to be continued. Some of the specific target molecules during the next budget year are: vitamin A isomers containing the 7,11-dicis geometry, 7-cis vitamin A2 isomers and Beta-carotene isomers containing the 7-cis and 7,7'-dicis geometry. New synthetic routes, stereoselective or not, will be explored in order to find conditions to yield pure isomers in large quantities. Spectroscopic and photochemical properties of the 7-cis isomers will be continually examined in detail. Our studies of rhodopsin analogs isolation and identification of pure geometric isomers of fluorinated retinals will be continued. These isomers will be tested as to their possible interaction with opsin. Other analogs include aromatic end group and dihydroderivatives. The bleaching of 7-cis analogs of rhodopsin will be investigated with kinetic and spectroscopic flash photolytic methods. We are now reaching the final stage of installation of the instrument. Parallel to the latter study will be studies of retinal triplets at low temperatures. BIBLIOGRAPHIC REFERENCES: V. Ramamurthy and R.S.H. Liu, "Photochemistry of Polyenes. IX. Excitation, Relaxation, and Deactivation of Dienes, Trienes, and Higher Polyenes in the Vitamin A Series in the Sensitized Isomerization Reaction," J. Am. Chem. Soc., 98, 2935 (1976). V. Ramamurthy and R.S.H. Liu, "Sigmatropic Hydrogen Migration and Electrocyclization Processes in Compounds in the Vitamin A Series. Photochemistry of Polyenes. X," J. Org. Chem., 41, 1862 (1976).